1. Field of the Invention
The present invention relates to a head position control method and a disk device for controlling the position of a read head or a read/write head on a rotating storage disk, and more particularly to a head position control method in a disk device having two or more heads of which each head corresponds to each one of the plurality of disk faces, and the disk device thereof.
2. Description of the Related Art
Disk devices using storage disks are widely used as storage devices. FIG. 36 is a diagram depicting the configuration of a conventional storage disk device. As FIG. 36 shows, the disk device is comprised of a disk 94 for storing data, a spindle motor 96 for rotating the disk 94, a head 90 for recording and regenerating information on the disk 94, and an actuator 92 for moving the head 90 to a target position. Typical disk devices are magnetic disk devices (HDD: Hard Disk Drive) and optical disk devices (DVD and MO).
In this disk device, position signals for detecting the position of the head 90 (position in track direction and radius direction) have been recorded on the disk 94. For example, in the magnetic disk 94, position signals 100 have been recorded for each sector 102 on a same circumference (track) of the magnetic disk, as shown in FIG. 38. The position signal has a track information which indicates the position in the radius direction of the disk 94, and sector information which indicates the position in the circumference direction of the disk 94.
The head 90 can detect the position of the head 90 in the radius direction and circumference direction by reading this position signal 100. Such a disk device has one head, and a displacement of the position signals between disks or between the disk faces does not occur if the device uses only one face of the disk.
However, if the disk device has two or more heads, and uses a plurality of disk faces (front and back of a disk, or a plurality of disks), a displacement of position signals becomes a problem, so this device is based on the following implicit assumption.
In other words, the track numbers of the position signals recorded on the disk 94 and the number of the position signals are common for all the heads. This means that the start position and end position of the data area in the radius direction of the disk are common. Also between heads, there is no displacement of the position signals in the radius direction, and between heads there is no displacement in the circumference direction.
However, if there is a displacement in the radius direction and circumference direction between the heads, when a first head is switched to a second head, the second head requests a control mode which is different from the first head to a same actuator.
Also after the device is assembled, the positional relationship of the position signals may become different, due to the displacement in the assembly of the disk after shipment from the factory. However, there are no devices where disks are displaced prior to this. So a position demodulation device or position demodulation method for such a device has been constituted based on this implicit assumption.
To implement such an implicit assumption, after the disk device is assembled, that is after the disk 94 is installed on the spindle motor 96 and the head 90 and the actuator 92 are mounted, servo track write (STW), which is an operation for recording servo signals (position signals) on the disk 94 by the head 90, is performed. In the present description, this conventionally performed STW method is called “conventional STW”. In other words, the above mentioned assumption is implemented by writing position signals after the positional relationships of the plurality of target heads and disks are fixed.
On the other hand, there is a method of performing STW (writing position signals on the disk 94) before assembly of the device. Since the disks are handled as a single disk, this method is called “media-level STW”. In the case of an HDD where this single disk STW method is applied, the above implicit assumption is not established.
In other words, when disks where position signals have been written in advance are installed in the disk device, the positional relationship between the position signals on each face of the disks and the head shift. One of these displacements is a displacement in the circumference direction. In this case, the detection timing of the servo signals and circumference positions of the servo sectors become different among each face of the disks. This influences the position demodulation circuit as a time difference.
The other displacement is a displacement in the radius direction. For this, it is necessary to adjust the data recording range for each device by minimizing the displacement between the disks.
FIG. 39 shows this displacement of position signals. This shows the status when two disks, 94-1 and 94-2, for which STW has been completed, are installed on the spindle motor 96. The eccentricity amount is the difference between the rotation center 98 of the spindle motor 96 and the rotation centers of the disks 94-1 and 94-2 during STW. Also servo signals are displaced in the radius direction and circumference direction between the disks 94-1 and 94-2.
FIG. 37 shows the status of the displacement of the magnetic heads 90-1 and 90-2. Since it is impossible to perfectly install a plurality of magnetic head 90-1 and 90-2 without a displacement, the displacement appears as a displacement in the radius direction and circumference direction.
Since the displacements shown in FIG. 37 and FIG. 39 occurs in this way, the displacement must be handled when the heads are switched, and various displacement correction technologies have been proposed. As such a prior art for correcting the displacement of servo signals between heads, “Head positioning control method of magnetic disk device and device thereof” was proposed in Japanese Patent No. 3,226,499 (date of registration: Aug. 31, 2001).
This proposal discloses a method for measuring and saving the difference of the detection times of the servo signals of each head, and correcting the servo detection gate time with the saved time difference. This method is effective when the displacement of the servo signals in the circumference direction is small, just like the case when the positional signals are simultaneously recorded on the front and back of the disk.
The necessity of a displacement correction in the radius direction is based on the technology for using the data area in the track direction at the maximum considering eccentricity. In other words, in a conventional device, track numbers detected by the head are directly used for positioning control. For example, when the position control circuit receives a seek instruction to command positioning to the No. 10000 track, the position control circuit positions the head to a position where the track number No. 10000 on the disk can be read.
With the above method, however, in some cases the area for recording and regenerating data becomes small. This is the case when disks cannot be replaced, and the servo signals were recorded on the disks before the device is assembled. In this case, the range where the actuator can be moved in the device and the range of the track numbers on the disk differ, depending on the difference of the individual disk devices and the difference of individual servo track writers (hereafter STW).
For example, the range is 5000 to 40000 for the disk device 1, and 7000 to 42000 for the disk device 2. In such a case, according to the conventional method, the range of the track numbers to be used for recording data is set to be narrow, considering the variation of all the devices. In the previous example, 7000 to 40000 is set.
To expand this range of the track numbers, Japanese Patent Laid-Open No. 2001-266454, “Head positioning control method of disk device and disk device” proposes to convert the track numbers instructed from the host device for each head and for each zone, so as to make the data range of each disk variable.
In such a device which expands the range of the track numbers, the above mentioned displacement of the servo signals in the radius direction influences the conversion of the track numbers.
These displacements of position signals in the circumference direction between disks or between disk faces can be solved by a conventional method, in the case of a device where the displacement of the position signals is small. However, if the displacement in the circumference direction between disks or between disk faces is large, as described in FIG. 39, the conventional method becomes a cause of dropping performance when the heads are switched.
At first, conventionally values detected by the head (sector positions) are directly used for the positions in the circumference direction. In other words, if information with the sector number No. 0 is detected from the disk, the sector number is regarded as No. 0. Or if an index signal is detected, the sector number is regarded as 0. This processing method is the same even if a device, where a plurality of disks are mounted, is used.
This method is effective because of the premise that the positions of the sector numbers in the circumference direction are aligned with all the heads when the servo track write (hereafter STW) is performed. In other words, the program or circuits of the device are constituted using this implicit assumption.
For the case when the positions in the circumference direction are displaced, a method called “staggered sector” is used. For this method as well, all the displacement amounts of the sector numbers between heads are the same among the same type of devices, since there is no difference depending on an individual device. For example, it is impossible that the displacement reaches 100 sectors. The position demodulation based on this implicit assumption is effective, because servo signals are recorded by a conventional STW method.
On the other hand, a method for transferring magnetic patterns by a magnetic transfer method or thermo-magnetic transfer method, and recording servo signals on the front and back of one disk has been proposed. For example, this method is proposed in IEEE Transactions on Magnetics, Vol. 37, No. 4, 2001, “Demodulation of Servo Track Signal Printed with a Lithographically Patterned Magnetic Disk”, (T. Ishida, et al). Even if a pattern is transferred to the front and back of one disk, it is extremely difficult to accurately align the positions of the servo signals.
The same problem also occurs in the case of recording servo signals externally and then the disk is installed in the device, such as with single disk STW. When the number of sectors in a track is increased to 300 sectors or 500 sectors, for example, it is possible that a dislocation in the circumference direction between the heads of the device for recording servo signals and a dislocation between the heads of the device exceed the distance equivalent to one sector.
Such a problem is more conspicuous for a disk device with two or more disks. Dislocation is a problem even on the front and back of one disk, but if two disks are used, a dislocation generated at installing the disks is added, which causes more of a dislocation between heads.
To correct such a dislocation of sectors, marks are drawn on the disk and the position must be adjusted such that the marks are accurately matched between disks when the servo signals are recorded and when the disks are mounted on the device. However, adding such a manufacturing step increases the manufacturing time and the manufacturing cost. Even if marks are drawn, the above mentioned mechanical dislocation cannot be avoided, so it is difficult to 100% match the servo signals and the sector numbers among a plurality of disks.
Therefore this problem could not be effectively handled in prior art. So if prior art is used, processing to resynchronize with the sector numbers on the disk is required each time the heads are switched.
This influence leads to an increase in wait time for recording and regenerating data. For example, in a device which does not have a dislocation, the sector numbers are continuous. If the heads are switched with a sample where the sector number is 0 with the head 0, the sector number becomes 1 with the head 2 in the next sample.
In the case of a device with a dislocation, on the other hand, the sector number shifts to sector number 10, for example, if the heads are switched. And the dislocation amount differs depending on the individual device. In such a case, problems occur when data is recorded and regenerated. In a conventional device, the premise is that sector numbers between the heads are aligned. So when the data is recorded and regenerated, an LBA (Logical Block Address) is assigned based on this assumption.
If the dislocation amount is different depending on the individual device, a wait time occurs until the position of the head reaches an expected position of the circumference direction. Therefore time for recording/regenerating delays. And this wait time differs depending on the individual device. This causes a problem where the time until recording/regenerating data becomes long, that is, the processing performance for recording/regenerating data drops.
Secondly, in the case of the above mentioned prior art, when a dislocation in the radius direction is corrected, an effective track number conversion method and a measurement method for determining the conversion values are not provided when a plurality of disks are used. Therefore prior art has a problem in terms of application to a plurality of disks.